Induced heating of continuously moving metal strip with pulsating magnetic flux



Aug. 31, 1948. R M- BAKER 2,448,012

INDUGED HEATING oF coNTINUoUsLT MOVING METAL STRIP WITHv PuLsATINGMAGNETIC FLUX Filed sept. 9, 1944 wlTNEsEs:

ATTORNEY Patented Aug. 31, 1948 2,448,012 INDUCED HEATING F CONTINUOUSLYMOVING MET AL STRIP WITH PULSAT- ING MAGNETIC FLUX Robert M.

Westinghous burgh, Pa., a corp Balzer,` Pittsburgh, Pa.,

e Electric Corporation,

oration'of Pennsylvania Application September 9,

16 Claims. (C1. 21913) My invention relate quency heating; but iserally, to high-fremore particularly directed to refinements ininduction-heating of elongated traveling non-magnetic material, such asstrips, sheets, plates, and the like, for the'pu'rpose of controllingthe quality or manner or the heating, or for maintaining the position ofthe material with respect to the field-establishing means, or both.

This invention is in the nature of a continuation-in-part oi myccpending patent-application, Serial No. 521,229, iiled February 5,1944, and of an improvement on the full disclosure thereof. It is alsorelated to my copending patent-application, Serial No. 513,260, iiledDecember '7, 1943.

My invention is herein described in connection -with a preferred form inwhich elongated coilable metallic strip is passed longitudinally, or inthe direction of its length, thro or alternating magnetic field forheat-treatment, the magnetic flux lines passing transversely through thefaces oi the strip and inducing electrical currents therein which heat'the strip, a form oi induction-heating generally designated astransverse-flux induction-heating. In the embodiment herein described,flux lines may be considered to pass through one face of the strip,through the strip, and then out of the 'other face.

A difficulty of heating non-magnetic strip-like material by means `of asubstantially uniform transverse iiux resides in the tendency of itslengthwise portions along and near the edges or thin side-surfaces ofthe strip to become hotter than its intermediate central portions. Forthe sake of brevity, I hereinafter call such portion, which includes theedge and inner contiguous material oi the strip for an extent short ofthe longitudinal center, as a border-portion. My associated application,Serial No. 521,229, shows and claims embodiments for counteracting ornullifying this tendency in a manner to cause the temperaturedistribution across the strip, from edge to edge, to be more uniform.One of the embodiments therein disclosed does this by providing weakerheat-inducing fields at the border-portions of the material.Speciilcally, this is done by displacing opposite cooperatingmagnetic-eld-producing field-structures so that they are laterally outof line. Another embodiment utilizes a fleld-aecting means, in the formof a shield or screen, along the longitudinal borders of the magneticeld, which, in a sense, absorbs the current-inducing effect of the`iield along the border-portions of the traveling strip. The aforesaidpatent-application, Serial No.

s, gen

ugh a pulsating y assgnor to East Pitts- 19454, Serial No. 553,381

521,229, places emphasis on and claims the former embodiment. Theinstant patent-application is more concerned with embodiments usingfieldscreening means for not only preventing excess heating of theborder-portions of the strip, but for the additional purpose ofcentering the strip between the field-producing field-structures.

Non-magnetic strip, such as aluminum or brass, for example, is for themost part self-centering when passed through a transverse-uxinduction-heating furnace, such as disclosed or reierred to in myaforesaid patent-application, Serial No. 521,229. However, there may bea tendency for strip passing between the eldstructures oi such a furnaceto rub against a pole-face, thereby scratching or otherwise marring thestrip. I reason that an electrical force is created along the edges ofthe strip by the currents induced therein, which tends to drive suchedges towar a field-structure. The current induce be considered to flowin oblong paths lying in the plane of the strip, These oblong paths havecurved ends or turns in the strip border-portions, with componentssubstantially paralleling the adjacent edge, and have straightconnecting-parts extending across the width of the strip, between theend-turns, as more particularly shown in Fig. 4 of mypatent-application, Serial No. 521,229. The current-now along thestraight connecting parts of the oblong path cooperates with leakageflux in the core-slots of the field-structures to provide a centeringeffect on moving non-magnetic strip in the air-gap, which tends to-center the non-magnetic strip between the field-structures, but thecurrent-flow in the end-turns'oi the oblong path reacts with theheat-inducing magnetic field thereat, giving rise to forces which tendto move the strip toward a field-structure. In any event, the strip maytend to bow crosswise in the work-passage. By the use of fieldaiectingmeans, or field-screening means, eX- tending over the edges of the stripalong the lengthwise borders of the air-gap, or work-passage, not onlyis overheating of the strip borderportions reduced but the tendency forthe strip to migrate toward a core is practically eliminated so that thestrip passes centrally through the induction-heating furnace.

An object of my invention resides in providing an induction-heatingfurnace for controllably electrically heating traveling elongatedstrip-like material.

Another object o viding an electrical furnace i my invention resides inprowhich produces a inducing means.

Still another object of myinventionv is to" provide an induction-heatingfurnace having laterally adjustable held-structures to one or both ofcurrents in these portions.

-Other objects, features and innovations of my invention will bediscernible from the following the accompanying generally schematic yandsimplied drawing, in which:

Yliigure 1 is a diagrammatic Fig. 6 is an enlarged sectional view,substantially on the line VI-VI of'Fig. v5, more clearly showing thecross-section of a preferred' screening-means; and

Fig. 7 is an elevational view'of a plate, secured to a field-structure,for supporting the screening means.

In Figures 1 and 2, a transverse-'flux inductionheating furnace is shownin a simplified form.

structures i and 2 having parallel ilatpole-'faces 3 and ll,respectivelyVspace'd kapart to form a shallow air-gap or work-passage 5.vThe eldcan be considered to pass from one pole-face to The strip passesdownwardly .together by :a v.cross-member l l tion, is a 'tromagneticnerd-structures I passage while the border-portions have a tendency tobe forced to a field-structure and also to overheat. For substantiallyreducing both ber 8 along each longitudinal border of the workpassage 5,having plate-like legs 9 and i0 on opposite sides of the associatedborder-portion of the strip.

Each member 8 comprises a U-shaped member comprising the plate-like legs9 and l0 joined Each leg has a free edge |.2.in the work-passage, sothat the Us'of themembers 8 face each other. Secured kto thecross-memberI i, in heat-exchanging relahollow member I3 cooling Iiuid may be passedfor removing heat introduced in the legs 9 and and 2 are energized toprovide the heat-inducing transverse ilux in the work-passage. Each ofthe legs 9 and have its free edge l2 serrated, as more strip'G and thefield-structures l and 2.

Figs. 3 and 4 show an induction-heatingfurnace having automatic meansfor changing `the lateral .positions of the held-structures forcontrolling the relative positions of lafield-structure and anadjacentstrip-edge, as more described and claimed in myaforesaidpatentapplication, Serial No. ally-movable eld-structures i9and'20 provide awork-passage 2| through which non-magnetic strip 22,having edges 23, moves downwardly after `passing around an upper roller`lll! which,

passage. Strip-moving means, represented by a pull-unit 26, pulls `thestrip through the induction-heating furnace.

yEach of the vfield-structures I9 and 20 comprises vcomb-shapedlaminations formed into a magnetic core 27 having like poles or teeth 28and like slots .29, alternating with each other. "Windings or coils 3Uare iiXed in the slots 29 and are so energized by any suitablealternatingcurrent source, connected to the.v coi1s.30, that a pole ononeeld-structure will have apolarity opposite to that of the directlyopposite pole on the other 'Held-structure, .as indicated `by theldesignations in Fig. 4. `field-structure is provided with a separatening-means`3i which the topA of .the...associatecl eld-structure forvproviding a light beam cutbya .strip-edge. -..A control rmeans v32, fassociated Witheach. scanning .means 3l, is ,electrically connectedthereto land respondsin accordance .with vthe extent, to which a stripborder-portion interruptsk the light beam. The response. correspondingly`controls .the ,en-

ergization of a reversi-ble .motor 33 fortheassooiated'field-structure.Energization oa motor from the closest edgeof the strip.

Y In `the embodiment of Figs. 1 and 2, 'the screening-means areseparate. from the eldstructures so that they can be'independentlyadjusted, but the screening-means can be xed or adjustably secured tothe field-structures, as shown in Figs. 3, 4 and 5. In this lastembodiment a screening-means 34 is secured to each field-structure formovement therewith. It comprises an elongated U-shaped member forcontrolling the effect of the transverse magnetic field on theborder-portions of the strip 22, and for separating or screening thistransverse magnetic eld from the field produced by the parts of theinduced currents flowing in the portion of the strip, which lies withinthe screening-means 34.

Fig. indicates, in a limited way, a practical form of a field-structurehaving a screeningmeans thereon. The field-structure comprises a framewhich includes top and bottom channelbars 35 and equally spacedframe-members 36. Lamlnations of a general form shown in Fig. 4 areclamped, in any suitable manner, between the frame-members 36 so as toprovide the core 21. The core has an outer planar pole-face consistingof the extremities of the teeth 28. A fieldstructure of this sort isdescribed in greater detail and claimed in the R. M. Baker et al.patentapplication, Serial No. 542,380, filed June 27, 1944.

A small plate 31 is secured to the upper channel-bar 35 and a smallplate 38 is secured to the lower channel-bar, the plates being along theside of the pole-face which is maintained relatively inside of astrip-edge. The plates 31 and 39 adjustably support the screening-means34 which comprises a relatively near plate-like member 39 and arelatively far plate-like member 40, considered with respect to thefield-structure with which they are associated. The members 39 and 40are of the same width with each having a straight free edge 4I at alongitudinal side of the screening means, which lies inside the magneticfield between the field-structures. The far member 40 is as long as thefield-structure, but the near member 39 is longer, having endsprotruding beyond the ends of the member 40, so that a screening-meanscan be secured to the plates 31 and 38 in a manner permitting its freeedges to be adjustably positioned parallel to or at a slant to thedirection of movement of the strip 22. To this end, the plate 31 has anelongated hole 42 for receiving anywhere therein a. fastening bolt of abolt and nut means 43. The bolt passes somewhat loosely through a roundhole 44 in the upper protruding end of the near member 39 which canswing thereon. The lower protruding end of the member 39 comprises acurved slot 45, centered on hole 44. Any part of the slot 45 can receivea bolt of a bolt and nut means 46. This last bolt passes through asomewhat enlarged hole 41 in the plate 38. By the use of suitablespacers and nuts for the boltY and nut means 43 and 46, the edges 4|ofthe screening-means 34 can be placed in various different positionswith respect to the associate fieldstructure, in an obvious manner. Thedashed line 4|' in Fig. 5 indicates an adjustment of the screening-meanswhich places its edge obliquely in the work-passage, with thescreening-means inserted further into the work-passage at the exit end.Preferably, the members 39 and 49 are equally spaced from the parallelmedian plane of the work-passage therebetween so that the members 39 and49 for each screening-means 34 lie on opposite sides of a border-portionof the strip 22. The members 39 and 49 are abuttingly welded, orotherwise secured in good thermal relation, to' a relatively heavy metalend-bar 48' of the same length as the member 39. Welded or soldered tothe outer surface of the bar 48 are a pair of hollow metal tubes havinga U-bend 49 joining their bottom ends so as to provide a continuouspassage for a cooling fluid which can be admitted and withdrawn from theother ends of the tubes.

The plate-like members 39 and 40 and also the bar 48 of thescreening-means are preferably, but not necessarily, of a metal having aresistivity vlower than that of the strip being heat-treated. Themembers 39 and 40 should have a thickness equal to at least that of the"depth of current penetration in centimeters. This depth of penetrationis usually considered equal to P 5030\/f where P'is the resistivity ofthe material of the members 39 and 49, in ohm-centimeters, and f is thefrequency in cycles-per-second at which the transverse magnetic fieldalternates or pulsates. The thicknesses of the members 39 and 40 can be,and preferably are, greater than the depth of penetration. If they aremade less, the transverse magnetic field between the fieldstructures, ineffect, penetrates the screeningmeans 34, so that some of the flux getsthrough for heating the edge-portions of the strip and reacting with thecurrent-flow therealong.

By means of tests an indication can be obtained of the manner in which astrip is heattreated when the screening-means occupies differentpositions. A hardness traverse across the width of the strip ispreferred for obtaining the temperature distribution therealong. Byvariously adjusting the screening-means, skill coming with experience,an adjustment can be found for a given material which will provide aheattreatment across the width of the strip of utilizable uniformity,within a variation in temperature which, from actual tests, l'.approximate at 5% for aluminum. I can not state exactly how far ascreening-means should overlap the strip. About one-third to one-half ofa pole pitch seems to be the average overlap for aluminum sheet with theextending portions of the screenmembers 3'9 and 49 extending laterallybeyond the end-bar 48 a width of about two-thirds of the pole pitch ofthe field-structures. If the overlap or the width of the extendingportion is insufficient the screening of the magnetic field may not beso thorough. If too great, more heat may be lost in the screening-meansthan is necessary. It is also desirable t0 skew the screening-means, sothat the straight edges 4| are oblique to the parallel frame-members 355and the length-direction of the teeth 23. This makes the effect of thescreening-means more gradual as the strip passes into and through theinduction-heating means.

The spacing between the members 39 and 40 Should be sufficient toreceive, with satisfactory working clearance, the thickest Istripexpected to be treated, but I prefer to make the spacing; greater sothat the members can be faced with an, insulating lining 5! withoutdecreasing the clear,` ance. Preferably, the lining is of some softinsulating material, such as absestos board, and at least as long as thefar member 4i) so that sparking between the metal of the screening-meansand the strip is minimized, and so that any occasional rubbing orcontact of the strip on the inner sides. of the screening-means will notseriously mar or 7 Scratch the Lsurfaces of y,strip :having Ysurfacenishes which must be protected during Aheattreatment. The extreme .edgeof` the strip `should also clear the `screen-bar 48 suincient tominimizetheepossibility of contact or vsparking therebetween.

While I havedescribed my invention in a manner understandable to thoseskilled in the art, an-d in forms which I now prefer, it is .apparentthat renements and improvements-.and other embodiments may be made,utilizing the teachings and principles of my invention hereinvdescribed.

I claim as my invention:

1. Transverse-flux heating-apparatus having a relatively shallow andWide work-passage for receiving elongated strip-like materialfor-heattreatment, said heating-apparatus comprising. in combination,means for establishing a pulsating magnetic eld across the shallow partof the work-passage, for introducing heat vinto the material, and meanscomprising a screen along a border of the work-passage, extending onlypartially across a wide side of the work-passage,'for screening bothfaces of a longitudinal edge-portion of the material from decrease thetendency for electromagnetic lreaction between said materialedge-portionand said eld to aiect the heating across the width of thematerial.

2. The combination with a transverse-flux induction-heating meansincluding a work-passage, and means for moving strip-like material in acertain direction through said work-passage, said induction-heatingmeans comprising linx-producing means having a distinct field-structureon i each side of said work-passage, for-providingfan alternatingmagnetic field in said Work-passage; ofa metallic screening-means alongaborderof the work-passage, for providing a field-screen betweensaidfield-structures, on the one hand, and a longitudinal portion alonganedgeof the material, on the other hand, said metallic screening-meanscomprising an elongated ynon-magnetic metallic member having an edgeinside the field, extending in said direction.

3. The invention of claim 2, characterized by said metallicscreening-means having passages for cooling fluid along a portionthereof which is opposite to its said edge.

4. The combination with a transverse-flux-induction-heating meansincluding a Work-passage, and means for moving strip-like-material ina,certain direction through said Work-passage, ysaid induction-heatingmeans comprising flux-producing means having a distinct field-structureon each side of said work-passage, for providing an alternating magneticrleld in-said work-passage; of a metallic screening-means along a borderof the work-passage, extending in said" direction, for screening aportion ofthe material from theel'd, said metallic screening-meanscomprising a nonmagnetic metallic memberfhaving an edgeinside the eld,extending in said direction, r.and

member to a field-structure. l5. The combination with atransverse-'Ilumineachy side of said work-passage, for providinganalternating magnetic iield in said work-passage;

along -each border said field, wherebyv to .f

member being between one of said field-struc'- tureswand :a medialpartof the .work-passage, wherebyto retain: the material centrally invsaid work-passage.

i6..The invention of claim 5, ycharacterized by said members having an:edge in said neld, and means for --removing heat :introduced `into said7. In combination.; a transverse-ilux inductionheating means including awork-passage through which strip-like ymaterial -can `bemovedlongitudinally, said induction-heating means comprisingflux-.producingmeans having a'eld-structureon eachside ofsaidwork-passage, for providing an `alternating magnetic neld in ,saidwork-passage, means for moving'one of said eld-structures-wth respect tothe other for changing theux 4distribution of saidiield in saidwork-passage.; and a screening-means along a longitudinal edgeof one ofsaid ield-structures'for screeni-ng aportionof the .material from. saidfield, said member .being attached to one of said field-structures.

8. In combination, a transverse-linx inductionheating means yincluding-awork-passage through which strip-like material can be movedlongitudinally, said induction-heatingmeans` comprising ilux-.producing`means having *a distinct fieldstructure oneach side 'of saidWork-passage, `for providing anal-ternating magneticeld in saidwork-passage, meansy for laterally moving one ofsaid-field-structureswith respect tothe other, and metallicscreening-means longitudinally along bothvsides of the work-passagef-forscreenyin gboth longitudinal portions of the material which are near andalong an edge thereof-from the field, yeach of saidmetallicscreening-means comprising two non-magnetic metallic members the `Iield,each of said screening-means ,being-secured to a diierent ,one of. saidfield-structures.

,9. The invention of` claim 8, vcharacterized by each of Isaid,screening-means having an edgein said eld `oblique tothe `direction -oftravel for saidmaterial.

10. In combination, a transverse-flux induction-heating means includinga Work-passage through which `strip-,like material can be movedlongitudinally, said induction-heating means comprising linx-producingmeans having .a distinct eld-structureon leach side of-.said VWork-`passage, for providing a pulsating magnetic eld in said work-passage,means for laterally Vmoving one of. said field-structures with respectt0 the other,.and metallic screening-means along each longitudinalborder of the work-passage, for screening :both longitudinal portions ofthe fmateriaLalong. its edges from the eld, each of 4saidscreening-means being generally U -shaped in cross-section and provided.with passages vfor cooling uid in.y the,.crossmember `of the U.

11. In combination, a,transverse-iiux induction-heating. means includinga work-passage through whicnstrip-like.material ca-n be movedlongitudinally, said. induation-heating `means comprisingfluxfproducingmeans having a eldstructure on each `side ofsaidwork-passage, for providing a4 pulsating magnetic eld in saidWorkpassage, supportingA means for supporting one of saideld-structuresfor movement laterally of said work-passageso `that; it canifollow'anedge of the moving strip-like material, and a screening-meanslongitudinally along the-Work-passage for screening a border portionofthe materialso that thel eld isscreened therefrom, saidscreening-means being attached to said movable eldstructure for movementtherewith.

12. An electromagnetic structure of a type described, comprising a corehaving a .plurality of alternating poles and slots, the pole-faces lyingin a generally flat surface, metallic field-screening means, and meansattaching said metallic held-screening means to said core in front ofsaid surface, said metallic screening-means being narrower than saidcore.

13. The invention of claim 12, characterized by said poles and slotsbeing elongated and generally parallel, and said metallicscreening-means comprising a non-magnetic metallic member spanning aplurality of poles and slots.

14. An invention including that of claim 13 but characterized further bysaid non-magnetic metallic member having an edge-portion obliquelypassing across the face of a plurality of said poles and slots.

15. The invention of claim 12, characterized by said .poles and slotbeing elongated and generally parallel, and said metallicscreening-means being elongated in a direction transverse to the lengthof said poles and along an edge of said core.

ROBERT M. BAKER.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date Frary May 10, 1921 Northrup May30, 1933 Adams Nov. 3, 1936 Ronci Aug. 2, 1938 Sessions July 30, 1940Stansel Dec. 3, 1940 Sherman et al Oct. 27, 1942

